Conventionally, a method for detecting a change in dielectric constant caused by the motion of an animal using an LC resonance circuit is adopted in order to measure the motion amount of a laboratory animal.
Also, a method of measuring the motion amount using optical sensors is adopted. However, the conventional methods and apparatuses suffer the following problems.
In the method of detecting a change in dielectric constant caused by a motion of an animal using an LC resonance circuit, when measurements are performed by a plurality of measuring apparatuses, it is actually difficult to maintain each measuring apparatus to the same sensitivity, and the detected dielectric constant is often influenced by the individual difference or action speed of a laboratory animal. In addition, since the detection sensitivity of the apparatus is inversely proportional to a square of the distance to an object to be measured, the detection sensitivity varies depending on the height in a standing posture of a laboratory animal occasionally affecting detected dielectric constant, For this reason, even in a single apparatus, the measurement results vary.
When a motion amount is measured using optical sensors, it is difficult to dispose optical sensors at high density in consideration of interferences of light among the optical sensors, and hence, small actions are hardly measured. In particular, a laboratory animal not only merely moves in the horizontal direction but also performs various actions, e.g., a standing action on hind legs at a given position. In this case, the animal may complete a standing action on the hind legs, as shown in FIG. 9 from a normal posture shown in FIG. 8, but sometimes may stay in a lower posture as shown in FIG. 10 and return to the normal posture, and repeat such an action. However, it is difficult for the conventional measuring apparatus using optical sensors to detect such an incomplete standing action as the optical sensors are not arranged at high density, resulting in poor measurement precision of the motion amount.
When a laboratory animal maintains its posture between a complete standing state and an incomplete standing state, a chattering phenomenon, in which the sensor electrically repeats ON and OFF states near an electrical threshold level at which the detection level of the sensor is turned on, occurs due to a delicate change in the animal's posture or an unstable light-shielding state for the optical sensors. This causes the number of times of standing is counted to have an abnormally large value far from an actual value.
Furthermore, in order to eliminate interferences of light among the sensors, light-emitting elements with high focusing characteristics and light-receiving elements with high sensitivity must be used, resulting in an expensive apparatus.